This invention relates to material machining devices; particularly to machining device comprising in combination coring, sawing and positioning means; and most particularly to such devices as are used to machine samples of composite materials such as asphalt concrete into solid right circular cylindrical test specimens of smaller dimensions or beams of rectangular cross section.
Composite materials, in particular those which have very hard inclusions in a relatively soft binder (e.g. carbon fiber in an epoxy matrix or rock in an asphalt matrix), are difficult to machine into acceptable specimens for subsequent measurement of their engineering properties under loading conditions.
The reason for this is two-fold:
(1) the binders are usually temperature dependent similar to polymers; and
(2) the usual methods are subject to errors because of the types of machines used.
As an illustrative, albeit non-limiting embodiment, the case of asphalt concrete will be further explored. Asphalt concrete is a mixture of a binder material and rock typically used in pavement construction. The most common material of this type is mixed and compacted while hot. In order to test the material for its engineering properties such as strength or modulus or Poisson""s ratio, the mixed and compacted material must be cooled and cut into a shape and surface smoothness suitable for instrumentation and testing. Water and/or extended periods stored in a refrigerator are the most common methods of cooling. Water may cool faster, but asphalt mixtures are sometimes adversely affected by the water, and wet surfaces may not be acceptable for the testing instrumentation method of choice. Cooling is generally required prior to cutting in order to maintain specimen shape during handling and clamping. Fundamentally, the cooling stiffens the material and makes the polymer-like binder component stiffness closer to the stiffness of the rock component of the composite material. Additional cooling and/or cleaning is generally required during the cutting operation for chip/dust removal. Even when cooled, there is still a difference in stiffness between the rock and the asphalt. In many cases, it is also true that the oversize compacted sample of the material has a variation in its fundamental properties such as air voids from one end to the other and from the center to the outside periphery on the radius. The variation is mostly near the outer compacted surfaces so that coring and sawing of a smaller test specimen from a compacted specimen of a larger first size/dimension often results in the smaller specimen having a more consistent (i.e. less variable) distribution of fundamental properties such as air voids.
A standard lathe type machine cannot effectively be used to remove the center core by single point cutting tool machining of the outer portion of the radius because the cutting tool will damage the material when it hits hard inclusions and those hard inclusions try, in turn, to break chemical and mechanical bonds with the asphalt material. The advantage that coring possesses for this reduction in diameter is that it uses diamond segments or a continuous diamond ring and the material on both sides of the ring is confined, so the damage from the cutting tool is minimized.
The most common shape for a test specimen of this material is a solid right circular cylinder. In order to obtain consistent surface textures and void distribution within the specimen, the cylinder is usually subjected to two cutting operations with relatively expensive diamond cutting tools such as those described by Kwang (U.S. Pat. 5,316,416 May 31, 1994). One cutting operation consists of coring of the circular cross section and the other cutting operation consists of cutting the ends such that they are parallel. The two cutting operations occur in whichever order is convenient and they are usually done with two different machines.
The coring operation is typically performed with a motor driven core barrel which is attached only at one end by a threaded component such as a nut welded to the back of the barrel. Usually the barrel is too long for the application because off-the-shelf core barrels and their mounting system are designed to core into thick pavement structures. This often leads to relatively large run-out and poor surface texture of the cored specimen. Even when using water as the cutting fluid, it is often found that the coring operation ends with the cut specimen lodged inside the core barrel causing some difficulty in removing the good specimen from the barrel since it must come out of the barrel from the same end that it went in.
The specimen ends are usually cut with a motor driven diamond saw. Typically, very large diameter blades are used (e.g. 14-24 inch diameter blades are often used on 4-6 inch diameter specimens). Since the starting sample may not be very much oversize in the length dimension, the sawing operation often takes place very close to the finished ends. Such processing generally results in unacceptable finished ends because the waste end cannot be gripped while sawing, and the large diameter saw blade tends to flex. Some saws have a single blade, others have two blades on a mandrel to simultaneously cut both ends and to try to ensure parallel ends in the finished product. U.S. Pat. No. 6,311,684 issued to Hodsden (Nov. 6, 2001) addresses the issue of reducing the diameter across which a saw must cut, however the stiffness of the wire saw loop in the out of plane direction is likely to result in unacceptable cut surfaces.
In both coring and sawing, the machines currently in use often have difficulty with holding the specimen and feeding the cutter into the specimen (or feeding the specimen into the cutter if the machine design requires that). Specimen clamping is usually accomplished with a standard parallel jaw vise or a xe2x80x9cVxe2x80x9d jaw on one side of the vise. In order to grip the specimen tight enough to resist the cutter throughout the cutting process, these methods often require clamping forces which result in damage to the specimen.
Potential solutions to this problem include fluid or pneumatic chucks such as those described in U.S. Pat. Nos. 6,299,179 issued to Sheffer (Oct. 9, 2001) and 6,272,956 issued to Schuettel (Aug. 14, 2001). However, fluid chucks have two notable disadvantages: they have an affinity for damaging abrasive particles especially if the fluid is hydraulic oil, and they are often manufactured so that a large piece cannot extend through the back of the chuck because the fluid pressure source and actuating mechanism are often positioned in this location to provide for axial actuation of the jaw mechanism.
The rotational speed of the motor driving the core barrel or the saw, and the feed rate of the cutter into the material being cut are interrelated components of the cutting operation that control the surface finish, accuracy, and precision of the final specimen. In many cases, the drive motor speed is fixed, and the feed control is either manual or done at a fixed rate. Improvements in the drilling operation have been provided by U.S. Pat. No. 6,186,248 issued to Silay and McKinley (Feb. 13, 2001), which teaches a closed loop control system for diamond core drilling that automatically controls penetration rate, weight on the drill bit and torque load applied to the drill string. This device fails to teach or suggest a device for coring and slicing of a specimen.
Thus, the disadvantages which exist in the prior art include the following:
1. Two separate machines are usually necessary to perform the two tasks of coring and slicing. This increases operator involvement in the preparation process and generally results in added costs in initial capital outlay, maintenance, and specimen preparation time.
2. Standard core barrels and saw blades are typically larger and more expensive than necessary to handle the task of cutting engineering test specimens. Not only is this unnecessary, the larger size can cause poor finished specimen geometries.
3. Typical clamping systems tend to induce specimen damage.
4. Because asphalt mixtures vary widely in their composition (e.g. in terms of the rock size and distribution, and the character of the binder), constant RPM motors are not appropriate unless some form of variable speed transmissions are also part of the machine.
5. Again, because of the widely varying composition of asphalt mixtures, manual and constant rate feed systems are not appropriate.
A material processing machine is presented comprising, in combination, at least one power generating means, which may be illustrated as a motor having varying properties, for example a single reversible variable speed motor and/or variable torque motor. Said motor will generally include a single drive shaft which, in one embodiment, allows optional mounting of three relatively inexpensive small diameter diamond saw blades adapted for cutting beams of rectangular cross section and transfers power to a bearing mounted work holding chuck, the work holding jaws of said chuck being centrifugally and torsionally actuated to contact the specimen, an actuator that moves an open-backed core barrel into the specimen held in the chuck, a finished test specimen and waste material ejection system, and actuators for advancing diamond segmented cutoff tools into the turning specimen held in the chuck.
Accordingly it is an objective of the instant invention to provide an apparatus for machining material with hard inclusions which obviates the disadvantages of prior machines.
It is a further objective of the instant invention to provide a device which is compact in size, enabling it to be used in crowded laboratories or for mobile applications.
It is a further objective of the instant invention to teach a device which combines the processes of coring and sawing the ends of a specimen into one machine.
It is still an additional objective of the instant invention to provide a device in which non-rotating cutting tools are advanced into the oversize sample to cut a cylindrical specimen of the required dimensions.
It is another objective of the instant invention to provide mounting means for optionally installing at least three rotating saw blades adapted for machining rectangular cross section beams at least two at a time, which can be made relatively economically, and which can be easily operated.
Still further objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.